On Saturday the Tasmanian Premier Lara Giddings announced that her government would introduce a Bill to allow same-sex marriage in that State. Giddings claimed she had legal opinions supporting the constitutionality of the measure, including from the Tasmanian Solicitor-General. UNSW constitutional law academic Professor George Williams has also written on the issue claiming State same-sex marriage legislation would be valid.
It is argued that State same-sex marriage legislation would be invalid because the Commonwealth Marriage Act 1961 (Cth), by providing for marriage to be a legal institution between and man and a woman to the exclusion of all others, would be inconsistent with any State legislation legalising same-sex marriage. Where there is an inconsistency between Commonwealth and State laws, the Commonwealth law prevails.
Greens leader Christine Milne has asked for a pledge from the Commonwealth government that if Tasmania were to pass the legislation, the Commonwealth would not challenge it. If the Commonwealth did not challenge the law, that would not necessarily guarantee that the legislation would be free from challenge. Usually, to bring a constitutional challenge a person has to have standing, that is, a real interest in the dispute. It may be difficult to see how a non-Commonwealth party could argue they had this interest. A person or organisation could seek the fiat of the Commonwealth Attorney-General and bring a relator action. This simply means that the Commonwealth bestows on that person or organisation the Commonwealth’s standing to bring the dispute. Another alternative is that the Court may put questions of standing ‘to one side’ provided the Commonwealth intervened in the dispute in support of the plaintiffs so as to provide a contradictor with standing. This is what happened in the recent Williams litigation where the National School Chaplaincy Program was challenged. (See more analysis on the High Court’s approach to standing in Williams here).
In their submission to the Senate Legal and Constitutional Affairs Committee in March this year, scholars from the University of Adelaide addressed the question of inconsistency between the Marriage Act and a possible State law on the question. The submission called on the Commonwealth to amend the Marriage Act to put beyond doubt the validity of State laws on an issue. If the Commonwealth is not able or willing to act, it should at least ensure the States can. Below is an extract from that submission.
State power to pass laws on same-sex marriage
Civil unions, available to heterosexual and homosexual couples, are now recognised under the laws of Tasmania, Victoria, the ACT and Queensland. Civil unions are (largely) functionally equivalent, although morally and symbolically quite different, to marriage. No State or Territory has, as yet, attempted to pass a law allowing same-sex marriage.
There has been a large amount of academic commentary on the question of whether, since the inclusion of the definition of marriage in the Marriage Act in 2004, the Commonwealth has now ‘covered the field’ of marriage.  If this is the case, the States are unable to pass valid laws in regard to same-sex marriage because of the operation of s 109 of the Constitution. Even if the legislation does not go so far as to cover the field in its current state, there is judicial authority to the effect that the marriage power can only support legislation that protects the institution of marriage.
We argue that, if the current Bill is not successful before the Commonwealth Parliament, the Parliament should, at least, amend the Marriage Act to allow the States and Territories to enter this field. This could be achieved by removing the prescriptive definition of ‘marriage’ in s 5 of the Act as a union of a man and a woman. A federal system can flourish only when the sub-national units (in Australia, the States and Territories) are able to legislate in a way that is responsive to their communities; when jurisdictions can legislatively experiment and express community values. Giving the States and Territories the power to legislate with respect to same-sex marriage would allow for federal experimentation and local governance to thrive. Such a move may result in the recognition of same-sex marriages in some jurisdictions and not others. No doubt this may cause some administrative difficulties (for example, couples who have entered into a same-sex marriage in a State jurisdiction may still fall under the federal de facto property settlement legislation). Nonetheless, these are not insurmountable problems (and have been considered, for example, in the United States); they must be weighed against the benefits of allowing local laws to develop in tune with community attitudes.
The amendment of the Marriage Act in this way would also allow for Australia to fulfil its obligations, mentioned earlier, under the Hague Convention of recognising same-sex marriages entered into in foreign jurisdictions. This is currently precluded by the definition limiting the institution to unions between a man and a woman, together with s 88EA of the Act, which makes it clear that a union solemnised in a foreign country between a same-sex couple ‘must not be recognised as a marriage in Australia’. The combined effect of these two sections means that Australia is currently in breach of its international obligations. We strongly recommend they are removed.
The Submission in Support of the Marriage Equality Amendment Bill 2010 was written jointly by Gabrielle Appleby, Dr Laura Grenfell, Anne Hewitt, Associate Professor Alexander Reilly and Professor John Williams of the Law School, University of Adelaide. It was supported by Dr Judith Bannister, Professor Lisa Hill, Cornelia Koch, Rebecca La Forgia, Nicole Lederer, Professor Rosemary Owens, Professor Ngaire Naffine, Beth Nosworthy, Dr Bernadette Richards, Professor Andrew Stewart, Kellie Toole, Dr Alex Wawryk, and Helen Wighton of the University of Adelaide.
 Relationships Act 2003 (Tas); Relationships Act 2008 (Vic); Civil Partnership Act 2008 (ACT); Civil Partnerships Act 2011 (Qld).
 See generally Dan Meagher, The Marriage Power and Same-sex Unions (2010 Gilbert and Tobin Constitutional Law Conference); Geoffrey Lindell, ‘Constitutional Issues Regarding Same-Sex Marriage: A Comparative Survey – North America and Australasia’ (2008) 30 Sydney Law Review 27, 43-4; Geoffrey Lindell, ‘State Legislative Power to enact Same-Sex Marriage Legislation, and the Effect of the Marriage Act 1961 (Cth) as Amended by the Marriage Amendment Act 2004 (Cth)’ (2006) 9 Constitutional Law and Policy Review 25, 27-8; Kristen Walker, ‘The Same-Sex Marriage Debate in Australia’ (2007) 11 International Journal of Human Rights 109, 118-9.
 In Attorney-General (Vic) v Commonwealth (1962) 107 CLR 529 (known as the Marriage Act case) the High Court held that the marriage power’s protection of the institution of marriage meant it excluded any laws purporting to legalise bigamous marriage. It is possible that such reasoning may apply to same-sex marriage (but see pp 5-8 of this submission on the differing approaches to constitutional interpretation). The Marriage Act case may mean that the Commonwealth would have the power to amend the Marriage Act to ensure it covered the field against State same-sex marriage legislation as part of the incidental aspect of the marriage power.